In response to the increasing seriousness of global environmental issues, energy issues, and the like, a solar cell is attracting attention as clean energy-generating means with no concern over depletion. In a case in which a solar cell is used outdoors such as on the roof of a building, it is usual to use the solar cell in a solar cell module form.
Generally, the solar cell module is manufactured in the following order. First, a crystalline solar cell element (hereinafter also referred to as a power generation element or a cell in some cases) formed of polycrystalline silicon or monocrystalline silicon, or a thin film-type solar cell element obtained by forming an extremely thin (several micrometers) film of amorphous silicon or crystal silicon on a glass substrate or the like is manufactured. Next, to obtain a crystalline solar cell module, a protective sheet (a transparent surface protective member) for the solar cell module, an encapsulating material for solar cell, the crystalline solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated. Meanwhile, to obtain a thin film-based solar cell module, a thin film-type solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated. After that, the solar cell module is manufactured using a lamination method or the like in which the above-described laminate is suctioned in a vacuum, heated and pressed. The solar cell module manufactured in the above-described manner is weather resistant and is also suitable for outdoor use such as on the roof of a building.
An ethylene/vinyl acetate copolymer (EVA) film is widely used as an encapsulating material for solar cell due to its excellent transparency, flexibility, adhesiveness, and the like. However, in a case in which an EVA composition was used as a constituent material for an encapsulating material for solar cell, there was a concern over the possibility of a component being generated by the decomposition of EVA such as acetic acid gas affecting a solar cell element. In addition, while satisfying the above-described properties, an ethylene/vinyl acetate copolymer had a high polarity of vinyl acetate in the ethylene/vinyl acetate copolymer and thus had an insufficient volume resistivity.
In contrast to the ethylene/vinyl acetate copolymer film, a sheet of the encapsulating material for solar cell has been proposed which contains an ethylene/vinyl acetate copolymer, an ionomer of an ethylene/unsaturated carboxylic acid copolymer, and an organic peroxide, does not cause the corrosion-induced deterioration of a solar cell element even in a case in which the solar cell element is used for a long period of time in a constant temperature and humidity condition, and does not cause the degradation of the power generation performance of the solar cell element (for example, refer to Patent Document 1).
In addition, a resin composition for an encapsulating material for solar cell has also been proposed which contains an ethylene/α-olefin copolymer, an ethylene functional group-containing monomer copolymer, and an organic peroxide, and has excellent extrusion productivity, transparency, heat resistance, and adhesiveness to glass (for example, refer to Patent Document 2).